yes, i sort of agree with SnoManSnow- there's nothing wrong with purchasing dead rock and putting it in your tank, but if you don't know what that rock has been through....i mean, the guy who had it might have blasted it with copper based meds....and then you'll have a real problem.
live rock will be a big part of the filtration in your reef. no one really knows exactly how long it takes for dead rock to become live. i mean, it's one thing to get covered with coralline, but when does it actually get beneficial bacteria?
i don't know the answer to that either, so i say to you again- IF YOU CAN AFFORD THE CASH OUT OF POCKET, leave the dead rock alone. if you can't afford to fill your tank with live rock, then you might consider the dead stuff as a supplement.
one more thing- with a 54 gallon tank, you're not going to have mega amounts of space to put rock, so you might pick and choose your pieces of rock very carefully, to make your best aquascaping. :wink: